A microfluidic system for evaluation of antioxidant capacity based on a peroxyoxalate chemiluminescence assay

A microfluidic system incorporating chemiluminescence detection is reported as a new tool for measuring antioxidant capacity. The detection is based on a peroxyoxalate chemiluminescence (PO-CL) assay with 9,10-bis-(phenylethynyl)anthracene (BPEA) as the fluorescent probe and hydrogen peroxide as the oxidant. Antioxidant plugs injected into the hydrogen peroxide stream result in inhibition of the CL emission which can be quantified and correlated with antioxidant capacity. The PO-CL assay is performed in 800-μm-wide and 800-μm-deep microchannels on a poly(dimethylsiloxane) (PDMS) microchip. Controlled injection of the antioxidant plugs is performed through an injection valve. Of the plant-food based antioxidants tested, β-carotene was found to be the most efficient hydrogen peroxide scavenger (SA _HP of 3.27 × 10⁻³ μmol⁻¹ L), followed by α-tocopherol (SA _HP of 2.36 × 10⁻³ μmol⁻¹ L) and quercetin (SA _HP of 0.31 × 10⁻³ μmol⁻¹ L). Although the method is inherently simple and rapid, excellent analytical performance is afforded in terms of sensitivity, dynamic range, and precision, with RSD values typically below 1.5%. We expect our microfluidic devices to be used for in-the-field antioxidant capacity screening of plant-sourced food and pharmaceutical supplements. Figure Assembled PDMS microchip sandwiched between two glass plates with the top plate containing capillary reservoirs     

A microfluidic chip based sequential injection system with trapped droplet liquid-liquid extraction and chemiluminescence detection

A microfluidic chip-based sequential injection system with trapped droplet liquid-liquid extraction preconcentration and chemiluminescence detection was developed for achieving high sensitivity with low reagent and sample consumption. The microfabricated glass lab-chip had a 35 mm long extraction channel, with 134 shrunken opening rectangular recesses (L 100 microm x W 50 microm x D 25 microm) arrayed within a 1 mm length on both sides of the middle section of the channel. Ketonic peroxyoxalate ester solution was filled in the recesses forming organic droplets, and keeping the aqueous sample solution flowing continuously in the extraction channel; analytes were transferred from the aqueous phase into the droplets through molecular diffusion. After liquid-liquid extraction preconcentration, catalyst and hydrogen peroxide solutions were introduced into the channel, and mixed with analytes and peroxyoxalate ester to emit chemiluminescence light. The performance of the system was tested using butyl rhodamine B, yielding a precision of 4% RSD (n = 5) and a detection limit of 10(-9) M. Within a 17 min analytical cycle, the consumptions of sample and peroxyoxalate solutions were 2.7 microL and 160 nL, respectively.     

A microfluidic glucose sensor incorporating a novel thread‐based electrode system

An electrochemical sensor for the detection of glucose using thread‐based electrodes and fabric is described. This device is relatively simple to fabricate and can be used for multiple readings after washing with ethanol. The fabrication of the chip consisted of two steps. First, three thread‐based electrodes (reference, working, and counter) were fabricated by painting pieces of nylon thread with either layered silver ink and carbon ink or silver/silver chloride ink. The threads were then woven into a fabric chip with a beeswax barrier molded around the edges in order to prevent leaks from the tested solutions. A thread‐based working electrode consisting of one layer of silver underneath two layers of carbon was selected to fabricate the final sensor system. Using the chip, a PBS solution containing glucose oxidase (GOx) (10 mg/mL), potassium ferricyanide (K₃[Fe(CN)₆]) (10 mg/mL) as mediator, and different concentrations of glucose (0‐25 mM), was measured by cyclic voltammetry (CV). It was found that the current output from the oxidation of glucose was proportional to the glucose concentrations. This thread‐based electrode system is a viable sensor platform for detecting glucose in the physiological range.     

氯丙嗪分子印迹化学发光微流控传感器芯片的研究

以氯丙嗪分子印迹聚合物为识别物质,以鲁米诺-K3Fe(CN)6化学发光体系,建立了一种新型的氯丙嗪化学发光微流控分子印迹传感器芯片的检测方法。利用二氧化碳激光在聚甲基丙烯酸甲酯材质上刻蚀出200μm宽,150μm深的微通道,8 mm长,1 mm宽,0.5 mm深的微检测池。微检测池中填充50μm粒径大小的热聚合得到的氯丙嗪分子印迹聚合物作为识别物质,在线富集氯丙嗪,富集的氯丙嗪可以增强鲁米诺和K3Fe(CN)6的化学发光强度,以化学发光强度定量氯丙嗪量。该传感器的响应值与0.02~0.4μg/mL氯丙嗪呈良好的线性关系,检出限为8 ng/mL(3σ)。该微流控传感器芯片已用于测定人尿液中的氯丙嗪。     

A methane gas sensor based on oxidizing bacteria

A bacterial sensor system based on Methylomonas flagellata AJ 3670 is described for methane determinations. The system consists of a bacterial, reactor, a reference reactor and two oxygen sensors. The current decreases with time until a steady state is reached within 30 s at 30°C; the maximum current difference is obtained at 30°C and pH 7.2. The response time for the determination of methane is less than 1 min. A linear relationship is obtained between the current difference and the methane concentration below 6.6 mM; the lower limit of determination is 5 μM, and the current decrease is reproducible within 5%. The current output of the sensor is almost stable for more than 10 days and 250 assays.     

A simple detection system for gas chromatography based on molecular absorption spectrometry in the gas phase

Summary A simple and inexpensive detection system for gas chromatography, based on gas-phase, molecular absorption measurements, is presented in which the chromatographic column is directly joined to the spectrophotometer flow cell, without heated transfer lines. A mixture of eight benzene compounds (including methyl, halogen and nitrogen derivatives) were separated and analyzed. Parameters affecting separation (temperature program and carrier gas flow) and measurement quality (wavelength and integration time) were studied and a measurement program designed to modify the wavelength during chromatography. The analytical characteristics of each compound were calculated, obtaining detection limits ranging from 0.5 to 9 g mL^–1. Finally, the method was applied to several synthetic mixtures, with good results.     

Development and characterization of a microfluidic glucose sensing system based on an enzymatic microreactor and chemiluminescence detection

Chemiluminescence detection was developed as an alternative to amperometric detection for glucose analysis in a portable, microfluidics-based continuous glucose monitoring system. Amperometric detection allows easy determination of hydrogen peroxide, a product of the glucose oxidase-catalyzed reaction of glucose with oxygen, by oxidation at a microelectrode. However, (micro)electrodes in direct contact with physiological sample are subject to electrode fouling, which leads to signal drift, decreased reproducibility and shortened detector lifetimes. Moreover, there are a few species present in the body (e.g. ascorbic acid, uric acid) which can undergo oxidation at the same applied potential as hydrogen peroxide. These species can thus interfere with the glucose measurement, reducing detection specificity. The rationale for exploring chemiluminescence as opposed to amperometric detection is thus to attempt to improve the lifetime and reproducibility of glucose analysis for monitoring purposes, while reducing interference caused by other chemicals in the body. The study reported here represents a first step in this direction, namely the realization of a microfluidic device with integrated silicon photodiode for chemiluminescence detection of glucose. This microflow device uses a chaotic mixing approach to perform enzymatic conversion of glucose, followed by reaction of the hydrogen peroxide produced with luminol to produce light at 425 nm. The chemiluminescence reaction is catalyzed by horseradish peroxidase in the presence of iodophenol. The performance of the fabricated chip was characterized to establish optimal reaction conditions with respect to sample and reagent flow rates, pH, and concentrations. A linear calibration curve was obtained for current response as a function of glucose concentration in the clinically relevant range between 2 and 10 mM, with a sensitivity of 39 pA/mM (R = 0.9963, one device, n = 3) and a limit of detection of 230 μM (S/N = 3).     

A magnetically active microfluidic device for chemiluminescence bioassays

Highly active horseradish peroxidase functionalized magnetic nanoparticles were prepared and packed into a microfluidic channel, producing an in-line bioreactor that enabled a sensitive chemiluminescence assay of H(2)O(2). The proposed magnetically active microfluidic device proved useful for chemiluminescence assays of biomedically interesting compounds.     

The use of a micropump based on capillary and evaporation effects in a microfluidic flow injection chemiluminescence system

The performance of a micropump operating on evaporation and capillary effects, developed for microfluidic (lab-on-a-chip) systems, was studied employing it as the fluid drive in a microfluidic flow injection (FI) system, with chemiluminescence (CL) detection. The micropump featured simple structure, small dimensions, low fabrication cost and stable and adjustable flow-rates during long working periods. Using a micropump with 6.6 cm² evaporation area, with the ambient temperature and relative humidity fluctuating within 2 h in the ranges 20-21 °C and 30-32%, respectively, an average flow-rate of 3.02 μL/min was obtained, with a precision better than 1.2% R.S.D. (n = 61). When applied to the microchip FI-CL system using the luminol/hexacyanoferrate/H₂O₂ reaction, a precision of 1.4% R.S.D. (n = 11) was obtained for luminol at a sampling frequency of 30 h⁻¹.     

A chemiluminescence array sensor based on graphene-magnetite-molecularly imprinted polymers for determination of benzenediol isomers

A chemiluminescence (CL) array sensor for determination of benzenediol isomers simultaneously using the system of luminol–NaOH–H₂O₂ based on a graphene-magnetite-molecularly imprinted polymer (GM-MIP) is described. Use of graphene in the GM-MIP thus prepared is helpful to improve the adsorption capacity, while use of magnetite nanoparticles can facilitate the isolation of GM-MIP at end of their synthesis, and rendering easier the use of the polymers in the array sensor. The adsorption performance and properties were characterized. The GM-MIP was used to increase the selectivity in CL analysis. In addition, the sensor was reusable and of good selectivity and adsorption capacity. The array sensor was finally used for the determination of hydroquinone, resorcinol and catechol in waste water samples simultaneously.     

Development of a chemiluminescence ethanol sensor based on nanosized ZrO2

Chemiluminescence was observed on introducing ethanol vapor to the surface of nanosized ZrO2 and this effect could be utilized to design a sensor for trace ethanol detection. The term cataluminescence (CTL) was used to describe this kind of chemiluminescence because the luminescence is generated by the catalytic oxidation of organic vapors on the solid surface. The proposed sensor showed high sensitivity to ethanol at 195 degrees C. The stability of the gas sensor was demonstrated by continuous reaction with ethanol for 100 h. Quantitative analysis was performed at an optimum wavelength of 460 +/- 10 nm. The chemiluminescence intensity was proportional to the concentration of ethanol from 1.6 to 160 microg ml(-1), with a detection limit of 0.6 microg ml(-1) (signal-to-noise ratio = 3:1). The mechanism of the chemiluminescence reaction is discussed and the results show that one of the possible luminescent intermediates is acetaldehyde. The chemiluminescence on nanosized ZrO2 observed in this work demonstrates the possibility of developing new nanomaterials for low-temperature cataluminescence detection.     

A simple thiourea based colorimetric sensor for cyanide anion

A simple and easily synthesized colorimetric anion sensor, based on a thiourea moiety as a binding subunit on a 1,2-cyclohexane backbone and a p-nitrophenyl group as a signaling unit, has been synthesized in a one step procedure. The selective sensing of anions, particularly cyanide, has been investigated in DMSO by UV-vis titration, ¹H NMR titration techniques and through ‘naked eye’ observation experiments.     

CMOS arrays as chemiluminescence detectors on microfluidic devices

A simple, low-cost process to integrate complementary metal oxide semiconductor array detectors (CMOSAD) for chemiluminescence is presented, evaluated, and applied to the determination of nitrite in ground water samples. CMOS arrays of different brands (obtained from commercial image sensors) were adapted as chemiluminescence detectors on microfluidic devices. The performance of the CMOSADs was evaluated in the visible zone of the spectrum using a tungsten halogen lamp as light source. Intrinsic parameters assessed included signal stability, spectral response, dark current, and signal-to-noise ratio. Thereafter, the CMOSADs were integrated on microfluidic devices and their performances in quantitative analysis were assessed with the chemiluminometric reaction of hydrogen peroxide with luminol, catalyzed with hexacyanoferrate (III). The parameters assessed were sensitivity, linear range, detection limit, reproducibility, correlation coefficient of the calibration curves, and baseline drift during measurements. The CMOSAD with the best performance was selected to assess the applicability of the developed microfluidic devices with the integrated detector. The microfluidic system permitted the determination of nitrite with both good precision and good recovery values in the analysis of ground water samples. Integration was easily achieved and enabled the development of a simple, low-cost, and feasible alternative to conventional detectors.     

基于分子印迹聚合物的化学发光传感器测定尿样中的甲福明

合成了甲福明的分子印迹聚合物,以此聚合物为识别物质,在线分离富集甲福明,建立了一种测定甲福明的流动式化学发光但感器。N-溴代丁二酰亚胺(NBS)和荧光素与甲福明发生化学反应,产生强的化学发光。甲福明质量浓度在2×10-8~8×10-6g/mL范围内同发光强度成良好线性关系,方法的检出限为6×10-9g/mL,相对标准偏差小于5%(n=9)。选择性实验表明将分子印迹聚合物作为识别物质应用于化学发光分析中,能大大提高化学发光分析方法的选择性。该传感器可逆性强、稳定性好,可重复使用100次以上,已用于人体尿样中甲福明的测定。     

流通式化学发光传感器测定亚硫酸根

基于酸性介质中高锰酸钾氧化亚硫酸根产生化学发光,喹咛具有较强的增敏作用,设计出了流通式化学发光传感器。该传感器对亚硫酸根的线性响应范围为1.0×10-7～5.0×10-4g mL,检出限为5×10-8g mL,对1.0×10-6g mL的亚硫酸根进行11次连续测定,相对标准偏差为3.5%。从取样到测定的全部分析过程只需1min。作为分子识别和换能作用的离子交换柱,可连续使用200次以上。方法已用于啤酒中亚硫酸根的测定。     

Flow chemiluminescence sensor for determination of clenbuterol based on molecularly imprinted polymer

In this paper, a novel flow chemiluminescence (CL) clenbuterol sensor based on molecularly imprinted polymer (MIP) on line enrichment nanogram clenbuterol and chemiluminescence reaction of potassium permanganate and formaldehyde in the polyphosphate enhanced by clenbuterol. Clenbuterol in the urine was selectively adsorbed on the clenbuterol-imprinted polymer, which was packed into the flow cell. The formaldehyde and the polyphosphate with potassium permanganate flowed through the flow cell and reacted with the on line adsorbed clenbuterol and produced strong CL. The results show that the sensor was reversible. The CL intensity was linear with clenbuterol concentration from 1.0 × 10⁻⁹ g/mL to 5.0 × 10⁻⁸ g/mL. The detection limit was 3.0 × 10⁻¹⁰ g/mL. The R.S.D. for ng/mL clenbuterol was less than 5% (n = 3). The present method offered a high selectivity and sensitivity that made the quantitative analysis of trace clenbuterol (ng/mL) in the animal urine sample.     

Interfacial organic synthesis in a simple droplet-based microfluidic system

A spherical liquid-liquid interface can be obtained by dispersing one liquid phase into another to form droplets, which will facilitate the two-phase reactions between the immiscible participating fluids. The phase transfer catalysts assembled at the droplet "wall" catalyze the reactions between the aqueous and organic phases. The study illustrates an interfacial synthetic approach which is ideal for the biphasic reaction by taking advantage of the droplet-based microdevice. The improved reaction efficiency can be attributed to the high surface-to-volume ratio and internal flow circulation in the droplets.     

A novel high selectivity chemiluminescence sensor for fenvalerate based on double-sided hollow molecularly imprinted materials

Novel fenvalerate double-sided hollow molecularly imprinted microspheres (fenvalerate-DHMIMs) were fabricated by in situ polymerization with the help of mesoporous silica microspheres (MSMs) in this paper for the very first time. Scanning electron microscope was employed to characterize the surface morphology of the fenvalerate-DHMIMs. Taking advantage of the quenching effect of fenvalerate on the luminol-H(2)O(2)-NaOH chemiluminescence system, a new model was established to determine fenvalerate by a highly selective flow injection chemiluminescence method. The traditional flow-through cell was replaced by a novel Y-shaped column. The chemiluminescence intensity was linear with fenvalerate concentration over the range of 5.0 × 10(-8) to 2.0 × 10(-5) g mL(-1) and the detection limit was 2.2 × 10(-8) g mL(-1). The relative standard deviation (RSD) for the determination of 2.0 × 10(-6) g mL(-1) fenvalerate was 1.4% (n = 11). The proposed method was applied to the determination of fenvalerate in real samples with satisfactory results.     

A cataluminescence gas sensor for carbon tetrachloride based on nanosized ZnS

A novel and sensitive gas sensor was proposed for the determination of carbon tetrachloride based on its cataluminescence (CTL) by oxidation in the air on the surface of nanosized ZnS. The luminescence characteristics and the optimal conditions were investigated in detail. Under the optimized conditions, the linear range of the CTL intensity versus the concentration of carbon tetrachloride was 0.4-114 μg mL⁻¹, with a correlation coefficient (R) of 0.9986 and a limit of detection (S/N = 3) of 0.2 μg mL⁻¹. The relative standard deviation (R.S.D.) for 5.9 μg mL⁻¹ carbon tetrachloride was 2.9% (n = 5). There was no or weak response to common foreign substances including methanol, ethanol, benzene, acetone, formaldehyde, acetaldehyde, dichloromethane, xylene, ammonia and trichloromethane. There was no significant change of the catalytic activity of the sensor for 40 h over 4 days, with a R.S.D. of less than 5% by collecting the CTL intensity once an hour. The proposed method was simple and sensitive, with a potential of detecting carbon tetrachloride in environment and industry grounds. The possible mechanism was also discussed briefly.